1. Field of the Invention
The present invention relates generally to methods and apparatus for scribing and breaking semiconductor devices into individual dies. In particular, the invention relates to scribing machines that use a hoop and film assembly to support the semiconductor devices in position beneath a scribing tool. More particularly, the invention relates to adapter plates for receiving and supporting the hoop and film assembly and limiting the movement of the film relative to the scribing tool.
2. Description of the Related Art
In the manufacture of microelectronic devices such as semiconductor lasers, many lasers are fabricated on a single bar. The bar is separated into individual lasers using semiconductor scribing and breaking equipment.
Semiconductor scribing equipment includes sharp pointed scribes. The scribes are drawn across the surface of the bar to scribe a line or lines along which the bar is eventually broken into individual lasers. Examples of semiconductor scribing and breaking equipment are shown in U.S. Pat. No. 5,820,006, U.S. Pat. No. 4,653,680, and U.S. Pat. No. 4,095,344, the entire disclosures of which are incorporated herein by reference.
In the apparatus disclosed in U.S. Pat. No. 5,820,006 and U.S. Pat. No. 4,653,580 a wafer-holding chuck is motor driven in an X direction and a Y direction and rotates about an axis perpendicular to the X and Y directions. At a scribing station, a scribe module is mounted above the wafer-holding chuck. An impulse bar with a straight sharp upper edge is mounted beneath the wafer-holding chuck and is carried along with the chuck. During scribing, the chuck carries a wafer to the scribing station at which time the upper sharp edge of the impulse bar rises to apply force against the bottom surface of the wafer along a line in the X direction and place the top surface of the wafer in tension. While the top surface is under tension, the wafer is moved relative to the scribe in the X direction to scribe the wafer in a line directly above the elongated sharp edge of the impulse bar. After the first scribe line is completed, the wafer is moved a predetermined distance in the Y direction and the wafer is scribed again along a line parallel to the first scribe line. When all of the desired X direction scribe lines are scribed, the chuck is rotated 90.degree.. The process is repeated, thereby providing a plurality of scribe marks in the X and Y directions. The scribe marks in the X and Y directions cooperate to define a plurality of individual dies.
Subsequent to scribing, the chuck transports the wafer to a breaking station where an anvil is moved to a predetermined distance above the wafer. The chuck positions the first scribe line above the sharp edge of the impulse bar and below the anvil. Once positioned, the impulse bar and is forced upwardly to pinch the wafer scribe line between the anvil and the sharp edge of the impulse bar, breaking the wafer along the scribe line. The wafer is moved a predetermined distance in the Y direction to align the next scribe line between the anvil and the impulse bar, and the breaking process is repeated. When the wafer is broken along all of the X direction scribe lines, the chuck is rotated 90.degree. and the process is repeated to break the wafer along the Y direction scribe lines.
In conventional equipment such as that disclosed in the '006 and '580 patents, a thin adhesive polymer film is stretched over a support ring, commonly referred to as a hoop assembly, and a wafer to be scribed is mounted on the adhesive film. The hoop assembly includes an inner hoop and an outer hoop that snaps over the inner hoop. The film is first stretched over the inner hoop and the outer hoop is then placed over the film and snapped in place, with the film being gripped between the two hoops.
In conventional operation, the hoop assembly is mounted on a chuck. The compliant film serves to seal a vacuum channel formed in the chuck and mechanically isolate the wafer from the vacuum ring and other surrounding rigid structures. The vacuum channel serves to retain the film and the wafer in position relative to the scribe.
This equipment is adequate for scribing and breaking wafers because the wafers are relatively large and rigid. Even though the wafers are mounted on a compliant surface, any movement due to the compliance of the film is within the required tolerances. Thus, the wafer can be positioned relative to the scribing tool, within required tolerances, by controlling the movement of the chuck.
The above-described equipment has been used to scribe wafers containing many types of semiconductor structure, including wafers containing semiconductor lasers. When semiconductor lasers are involved a wafer may contain many individual lasers which are to be separated. Typically, as many as 30 lasers are formed on a laser bar that measures only 12 mils wide by 300 mils long by 4 mils thick. Thus, each individual laser measures about 12 mils by 10 mills by 4 mils. Because the lasers are so small, the tolerances involved in scribing and breaking the lasers from the wafer are very tight. Unfortunately, sometimes the polymer film creeps slightly over the course of the scribing process, resulting in scribe lines that are out of tolerance for the lasers. As a consequence of imprecise scribing, many potential lasers are unusable and wasted.